The present invention relates to an electronic volume controller, and more particularly to a circuit for electronically controlling volume of an acoustic system.
The volume controller has a ladder attenuator comprising a plurality of resistors connected in series, and a plurality of switches corresponding to the resistors. The resistors are connected to an output one by one with the closing of corresponding switches, thereby decreasing the volume of a reproduced sound. The number of the resistors is determined in accordance with maximum attenuation and the amount of attenuation at each step. Namely, in order to attenuate the input signal thereto from 80 dB to 0 dB by 1 dB per step, eighty resistors and eighty one switches are required.
FIG. 10 shows an example of a conventional electronic volume controller 1. The input terminal of the volume controller is connected to a ladder attenuator 2 through a buffer amplifier 6. The ladder attenuator 2 comprises a series of resistors 2a each of which is connected to a corresponding analog switch 3 so that the resistance of the ladder attenuator 2 is changed from 0 dB to 70 dB by 10 dB per step.
The volume controller 1 further has a ladder attenuator 4 which is parallely connected to the ladder attenuator 2 through a buffer amplifier 8. Each resistor 4a of the ladder attenuator 4 is connected to a corresponding analog switch 5 to attenuate the volume from 0 dB to 9 dB by 1 dB per step, thereby finely changing the volume.
A loudness circuit 7 comprising resistors Ra and Rb and capacitors Ca and Cb is connected to both ends of the ladder attenuator 2. A loudness tap of the loudness circuit 7 is connected to one of the analog switches 3 which corresponds to the switch for -20 dB.
The switches 5 are selectively closed from 0 dB, thereby increasing the attenuation from 0 to -9 dB.
For example, when obtaining the attenuation of -22 dB, switches 3 corresponding to -20 dB are closed, and the switches 5 corresponding to -2 dB are closed.
The ladder attenuator 2 connected to the loudness circuit 7 is constructed to increase the attenuation by 10 dB. Therefore, when only the ladder attenuator 2 is operated, the volume is largely increased at each step, which gives unpleasant feeling to a listener.